Touch sensitive device with stylus support

ABSTRACT

A touch-sensitive device with stylus includes a touch panel, a stylus drive unit, a touch panel sense unit, and a measurement unit. A touch by a stylus proximate to a touch panel electrode changes a capacitive coupling between the touch panel electrode and a stylus electrode. The amplitude of the response signal is responsive to the capacitive coupling between the touch panel electrode and the stylus electrode, and is measured to provide an indication of the position of the stylus electrode relative to the touch panel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Patent Application Ser. No.61/182,366, “High Speed Multi-Touch Device and Controller Therefor”,filed May 29, 2009; and U.S. Patent Application Ser. No. 61/231,471,“High Speed Multi-Touch Device and Controller Therefor” filed Aug. 5,2009, and U.S. patent application Ser. No. 12/652,343, “High Speed NoiseTolerant Multi-Touch Device and Controller Therefor” filed Jan. 5, 2010.

FIELD OF THE INVENTION

This invention relates generally to touch-sensitive devices,particularly those that rely on a capacitive coupling between a user'sfinger or other touch implement and the touch device, with particularapplication to such devices that are capable of detecting multipletouches (from fingers and styli) applied to different portions of thetouch device possible at the same time.

BACKGROUND

Touch sensitive devices allow a user to conveniently interface withelectronic systems and displays by reducing or eliminating the need formechanical buttons, keypads, keyboards, and pointing devices. Forexample, a user can carry out a complicated sequence of instructions bysimply touching an on-display touch screen at a location identified byan icon.

There are several types of technologies for implementing a touchsensitive device including, for example, resistive, infrared,capacitive, surface acoustic wave, electromagnetic, near field imaging,etc. Capacitive touch sensing devices have been found to work well in anumber of applications. In many touch sensitive devices, the input issensed when a conductive object in the sensor is capacitively coupled toa conductive touch implement such as a user's finger. Generally,whenever two electrically conductive members come into proximity withone another without actually touching, a capacitance is formedtherebetween. In the case of a capacitive touch sensitive device, as anobject such as a finger approaches the touch sensing surface, a tinycapacitance forms between the object and the sensing points in closeproximity to the object. By detecting changes in capacitance at each ofthe sensing points and noting the position of the sensing points, thesensing circuit can recognize multiple objects and determine thecharacteristics of the object as it is moved across the touch surface.

There are two known techniques used to capacitively measure touch. Thefirst is to measure capacitance-to-ground, whereby a signal is appliedto an electrode. A touch in proximity to the electrode causes signalcurrent to flow from the electrode, through an object such as a finger,to electrical ground.

The second technique used to capacitively measure touch is throughmutual capacitance. Mutual capacitance touch screens apply a signal to adriven electrode, which is capacitively coupled to a receiver electrodeby an electric field. Signal coupling between the two electrodes isreduced by an object in proximity, which reduces the capacitivecoupling.

Within the context of the second technique, various additionaltechniques have been used to measure the mutual capacitance betweenelectrodes. In one such technique, a capacitor coupled to a receiverelectrode is used to accumulate multiple charges associated withmultiple pulses of a drive signal. Each pulse of the drive signal thuscontributes only a small portion of the total charge built up on this“integrating capacitor”. Reference is made to U.S. Pat. No. 6,452,514(Philipp). This technique has good noise immunity, but its speed may belimited depending upon the number of pulses needed to charge theintegrating capacitor.

Touch screens may also support the resolution of the positions of one ormore styli. Reference is made to U.S. Pat. No. 5,790,106 (Hirano), whichdescribes applying a voltage oscillating from a pen to electrodes in atouch panel.

BRIEF SUMMARY

The present application discloses, inter alia, touch-sensitive devicescapable of detecting the presence of one or more objects, includingfingers and styli, located proximate to, or touching, different portionsof the touch device, at the same time or at overlapping times. In someembodiments, the touch-sensitive devices need not employ an integratingcapacitor in order to measure the capacitive coupling between the driveelectrodes and the receive electrodes (associated with the touch panelor the stylus). Rather, in at least some embodiments, a single pulsefrom a drive signal may be all that is necessary to measure thecapacitive coupling between a particular drive electrode (which may bearranged in the stylus or in a the touch sensitive device) and aparticular receive electrode (which too may be arranged in the stylus orin the touch sensitive device). To accomplish this, assuming a suitablepulse shape is used for the drive signal, differentiation circuits arepreferably coupled to receive electrodes, which in various embodimentsmay be arranged in a stylus or in a touch panel, so that adifferentiated representation of the drive signal, referred to as aresponse signal, is generated for each receive electrode. In anexemplary embodiment, each differentiation circuit may comprise anoperational amplifier (op amp) with a feedback resistor connectedbetween an inverting input of the op amp and the output of the op amp,with the inverting input also being connected to a given receiveelectrode. Other known differentiation circuit designs can also be used,so long as the circuit provides an output that includes in some form atleast an approximation of the derivative with respect to time of thedrive signal.

Related methods, systems, and articles are also discussed.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a touch device;

FIG. 2 is a schematic side view of a portion of a touch panel used in atouch device;

FIG. 3a is a schematic view of a touch device in which relevant driveand detection circuitry is shown in the context of one drive electrodeand one receive electrode capacitively coupled thereto;

FIG. 3b is a schematic view of a touch sensitive device similar to thatof FIG. 3a , but including additional circuitry to account fordifferences of signal strength on receiver electrodes;

FIG. 3c is a schematic view of a touch sensitive device similar to thatof FIG. 3a , but including additional circuitry to account for noisefrom, for example, a display;

FIG. 3d is a schematic view of a touch sensitive device similar to thatof FIG. 3a , but including additional circuitry to accommodate noisefrom, for example, a display;

FIG. 3e is a schematic view of a touch sensitive device similar to thatof FIG. 3a , but including additional circuitry to accommodate, forexample, a low impedance touch screen;

FIG. 4a is a graph of a drive signal and a corresponding (modeled)response signal for the touch device of FIG. 3a , wherein the drivesignal includes rectangle pulses and the response signal includesimpulse pulses;

FIG. 4b is a graph showing modeled waveforms for three drivenelectrodes, and associated response waveforms on three receiveelectrodes;

FIG. 5a is a graph similar to that of FIG. 4a but for a different drivesignal, the drive signal including ramped pulses and the response signalincluding rectangle-like pulses;

FIG. 5b is a graph showing modeled waveforms for three drivenelectrodes, and associated response waveforms on three receiveelectrodes, similar to FIG. 4 b;

FIG. 6a is a graph of still another drive signal and a schematicdepiction of an expected response signal for the touch device of FIG. 3a, the drive signal including ramped pulses and the response signalincluding rectangle pulses;

FIG. 6b is a graph showing modeled waveforms for three drivenelectrodes, and associated response waveforms on three receiveelectrodes, similar to FIGS. 4b and 5 b;

FIG. 7 is a graph of a drive signal and corresponding (modeled) responsesignal for the touch device of FIG. 3c , wherein the drive signalincludes rectangle pulses and the response signal includes impulsepulses;

FIG. 8 is a schematic view of a touch device that includes a touch panelhaving a 4×8 matrix of capacitively coupled electrodes, and variouscircuit components that can be used to detect multiple simultaneoustouches on the touch panel.

FIG. 9 is a schematic view of a stylus;

FIG. 10 is a schematic view of stylus electronics, including stylusreceive electronics that are similar to those shown in FIG. 3a , andalso including stylus drive electronics;

FIG. 11a is a flowchart illustrating a measurement sequence for a stylusthat includes both stylus receive electronics and stylus driveelectronics, and which receives signals emanating from the touch paneland provides signals to be received by the touch panel;

FIG. 11b is a schematic of a simplified mutual capacitive, matrix-typetouch screen having two sets of electrodes, the first set being D1 andD2, and the second set being R1 and R2, and having present thereon atouch from a finger (F) and from a stylus (S);

FIG. 12 is a flowchart illustrating a measurement sequence for a stylusthat is configured to provide signals from the stylus to the touchpanel, and the stylus touch panel is configured to receive said signalsand determine therefrom the position of the stylus on the touch panel;

FIG. 13 is a flowchart illustrating a measurement sequence for a stylusthat is configured to receive signals emanating from a touch panel, andthe touch panel is configured to provide signals, and a controller isconfigured to determine the position of the stylus based on the receivedsignals;

In the figures, like reference numerals designate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In FIG. 1, an exemplary touch device 110 is shown. The device 110includes a touch panel 112 connected to electronic circuitry, which forsimplicity is grouped together into a single schematic box labeled 114and referred to collectively as a controller.

The touch panel 112 is shown as having a 5×5 matrix of column electrodes116 a-e and row electrodes 118 a-e, but other numbers of electrodes andother matrix sizes can also be used. The panel 112 is typicallysubstantially transparent so that the user is able to view an object,such as the pixilated display of a computer, hand-held device, mobilephone, or other peripheral device, through the panel 112. The boundary120 represents the viewing area of the panel 112 and also preferably theviewing area of such a display, if used. The electrodes 116 a-e, 118 a-eare spatially distributed, from a plan view perspective, over theviewing area 120. For ease of illustration the electrodes are shown tobe wide and obtrusive, but in practice they may be relatively narrow andinconspicuous to the user. Further, they may be designed to havevariable widths, e.g., an increased width in the form of a diamond- orother-shaped pad in the vicinity of the nodes of the matrix in order toincrease the inter-electrode fringe field and thereby increase theeffect of a touch on the electrode-to-electrode capacitive coupling. Inexemplary embodiments the electrodes may be composed of indium tin oxide(ITO) or other suitable electrically conductive materials. From a depthperspective, the column electrodes may lie in a different plane than therow electrodes (from the perspective of FIG. 1, the column electrodes116 a-e lie underneath the row electrodes 118 a-e) such that nosignificant ohmic contact is made between column and row electrodes, andso that the only significant electrical coupling between a given columnelectrode and a given row electrode is capacitive coupling. The matrixof electrodes typically lies beneath a cover glass, plastic film, or thelike, so that the electrodes are protected from direct physical contactwith a user's finger or other touch-related implement. An exposedsurface of such a cover glass, film, or the like may be referred to as atouch surface. Additionally, in display-type applications, a back shieldmay be placed between the display and the touch panel 112. Such a backshield typically consists of a conductive ITO coating on a glass orfilm, and can be grounded or driven with a waveform that reduces signalcoupling into touch panel 112 from external electrical interferencesources. Other approaches to back shielding are known in the art. Ingeneral, a back shield reduces noise sensed by touch panel 112, which insome embodiments may provide improved touch sensitivity (e.g., abilityto sense a lighter touch) and faster response time. Back shields aresometimes used in conjunction with other noise reduction approaches,including spacing apart touch panel 112 and a display, as noise strengthfrom LCD displays, for example, rapidly decreases over distance. Inaddition to these techniques, other approaches to dealing with noiseproblems are discussed in reference to various embodiments, below.

The capacitive coupling between a given row and column electrode isprimarily a function of the geometry of the electrodes in the regionwhere the electrodes are closest together. Such regions correspond tothe “nodes” of the electrode matrix, some of which are labeled inFIG. 1. For example, capacitive coupling between column electrode 116 aand row electrode 118 d occurs primarily at node 122, and capacitivecoupling between column electrode 116 b and row electrode 118 e occursprimarily at node 124. The 5×5 matrix of FIG. 1 has 25 such nodes, anyone of which can be addressed by controller 114 via appropriateselection of one of the control lines 126, which individually couple therespective column electrodes 116 a-e to the controller, and appropriateselection of one of the control lines 128, which individually couple therespective row electrodes 118 a-e to the controller.

When a finger 130 of a user or other touch implement comes into contactor near-contact with the touch surface of the device 110, as shown attouch location 131, the finger capacitively couples to the electrodematrix. The finger draws charge from the matrix, particularly from thoseelectrodes lying closest to the touch location, and in doing so itchanges the coupling capacitance between the electrodes corresponding tothe nearest node(s). For example, the touch at touch location 131 liesnearest the node corresponding to electrodes 116 c/118 b. As describedfurther below, this change in coupling capacitance can be detected bycontroller 114 and interpreted as a touch at or near the 116 a/118 bnode. Preferably, the controller is configured to rapidly detect thechange in capacitance, if any, of all of the nodes of the matrix, and iscapable of analyzing the magnitudes of capacitance changes forneighboring nodes so as to accurately determine a touch location lyingbetween nodes by interpolation. Furthermore, the controller 114advantageously is designed to detect multiple distinct touches appliedto different portions of the touch device at the same time, or atoverlapping times. Thus, for example, if another finger 132 touches thetouch surface of the device 110 at touch location 133 simultaneouslywith the touch of finger 130, or if the respective touches at leasttemporally overlap, the controller is preferably capable of detectingthe positions 131, 133 of both such touches and providing such locationson a touch output 114 a. The number of distinct simultaneous ortemporally overlapping touches capable of being detected by controller114 is preferably not limited to 2, e.g., it may be 3, 4, or more,depending on the size of the electrode matrix.

As discussed further below, the controller 114 preferably employs avariety of circuit modules and components that enable it to rapidlydetermine the coupling capacitance at some or all of the nodes of theelectrode matrix. For example, the controller preferably includes atleast one signal generator or drive unit. The drive unit delivers adrive signal to one set of electrodes, referred to as drive electrodes.In the embodiment of FIG. 1, the column electrodes 116 a-e may be usedas drive electrodes, or the row electrodes 118 a-e may be so used. Thedrive signal is preferably delivered to one drive electrode at a time,e.g., in a scanned sequence from a first to a last drive electrode. Aseach such electrode is driven, the controller monitors the other set ofelectrodes, referred to as receive electrodes. The controller 114 mayinclude one or more sense units coupled to all of the receiveelectrodes. For each drive signal that is delivered to each driveelectrode, the sense unit(s) generate response signals for the pluralityof receive electrodes. Preferably, the sense unit(s) are designed suchthat each response signal comprises a differentiated representation ofthe drive signal. For example, if the drive signal is represented by afunction f(t), which may represent voltage as a function of time, thenthe response signal may be or comprise, at least approximately, afunction g(t), where g(t)=d f(t)/dt. In other words, g(t) is thederivative with respect to time of the drive signal f(t). Depending onthe design details of the circuitry used in the controller 114, theresponse signal may include: (1) g(t) alone; or (2) g(t) with a constantoffset (g(t)+a); or (3) g(t) with a multiplicative scaling factor(b*g(t)), the scaling factor capable of being positive or negative, andcapable of having a magnitude greater than 1, or less than 1 but greaterthan 0; or (4) combinations thereof, for example. In any case, anamplitude of the response signal is advantageously related to thecoupling capacitance between the drive electrode being driven and theparticular receive electrode being monitored. Of course, the amplitudeof g(t) is also proportional to the amplitude of the original functionf(t). Note that the amplitude of g(t) can be determined for a given nodeusing only a single pulse of a drive signal, if desired.

The controller may also include circuitry to identify and isolate theamplitude of the response signal. Exemplary circuit devices for thispurpose may include one or more peak detectors, sample/hold buffer,and/or low-pass filter, the selection of which may depend on the natureof the drive signal and the corresponding response signal. Thecontroller may also include one or more analog-to-digital converters(ADCs) to convert an analog amplitude to a digital format. One or moremultiplexers may also be used to avoid unnecessary duplication ofcircuit elements. Of course, the controller also preferably includes oneor more memory devices in which to store the measured amplitudes andassociated parameters, and a microprocessor to perform the necessarycalculations and control functions.

By measuring an amplitude of the response signal for each of the nodesin the electrode matrix, the controller can generate a matrix ofmeasured values related to the coupling capacitances for each of thenodes of the electrode matrix. These measured values can be compared toa similar matrix of previously obtained reference values in order todetermine which nodes, if any, have experienced a change in couplingcapacitance due to the presence of a touch.

Turning now to FIG. 2, we see there a schematic side view of a portionof a touch panel 210 for use in a touch device. The panel 210 includes afront layer 212, first electrode layer 214 comprising a first set ofelectrodes, insulating layer 216, second electrode layer 218 comprisinga second set of electrodes 218 a-e preferably orthogonal to the firstset of electrodes, and a rear layer 220. The exposed surface 212 a oflayer 212, or the exposed surface 220 a of layer 220, may be or comprisethe touch surface of the touch panel 210.

FIG. 3a depicts a touch device 310 in which relevant controllercircuitry, such as drive and detection circuitry, is shown in thecontext of a touch panel 312 having one drive electrode 314 and onereceive electrode 316 capacitively coupled thereto via couplingcapacitance C_(c). The reader will understand that this is ageneralization of a touch panel in which drive electrode 314 may be oneof a plurality of drive electrodes, and receive electrode 316 likewisemay be one of a plurality of receive electrodes, arranged in a matrix onthe touch panel.

Indeed, in one specific embodiment of interest capable of use with atleast some of the touch measurement techniques described herein, thetouch panel may comprise a 40×64 (40 rows, 64 columns) matrix devicehaving a 19 inch diagonal rectangular viewing area with a 16:10 aspectratio. In this case, the electrodes may have a uniform spacing of about0.25 inches. Due to the size of this embodiment, the electrodes may havesignificant stray impedances associated therewith, e.g., a resistance of40 K ohms for the row electrodes and 64 K ohms for the columnelectrodes. For good human factors touch response, the response time tomeasure the coupling capacitance at all 2,560 nodes of the matrix(40*64=2560) may, if desired, be made to be relatively fast, e.g., lessthan 20 or even less than 10 milliseconds. If the row electrodes areused as the drive electrodes and the column electrodes used as thereceive electrodes, and if all of the column electrodes are sampledsimultaneously, then the 40 rows of electrodes have, for example, 20msec (or 10 msec) to be scanned sequentially, for a time budget of 0.5msec (or 0.25 msec) per row electrode (drive electrode).

The drive electrode 314 and receive electrode 316 of FIG. 3a , which aredepicted by their electrical characteristics (in the form of lumpedcircuit element models) rather than by their physical characteristics,are representative of electrodes that may be found in a touch devicehaving a matrix smaller than 40×64, but this is not to be consideredlimiting. In this representative embodiment of FIG. 3a , the seriesresistances R shown in the lumped circuit models may each have values of10 K ohms, and the stray capacitances C shown in the lumped circuitmodels may each have values of 20 picofarads (pf), but of course thesevalues are not to be taken as limiting in any way. In thisrepresentative embodiment the coupling capacitance C_(c) is nominally 2pf, and the presence of a touch by a user's finger 318 at the nodebetween electrodes 314, 316 causes the coupling capacitance C_(c) todrop by about 25%, to a value of about 1.5 pf. Again, these values arenot to be taken as limiting.

In accordance with the controller described earlier, the touch device310 uses specific circuitry to interrogate the panel 312 so as todetermine the coupling capacitance C_(c) at each of the nodes of thepanel 312. In this regard, the reader will understand that thecontroller may determine the coupling capacitance by determining thevalue of a parameter that is indicative of, or responsive to, thecoupling capacitance, e.g., an amplitude of a response signal asmentioned above and described further below. To accomplish this task,the device 310 preferably includes: a low impedance drive unit 320coupled to the drive electrode 314; a sense unit 322 coupled to thereceive electrode 316, which, in combination with the couplingcapacitance, performs a differentiation on the drive signal supplied bythe drive unit; and an analog-to-digital converter (ADC) unit 324 thatconverts an amplitude of the response signal generated by the sense unit322 into a digital format. Depending on the nature of the drive signalsupplied by the drive unit 320 (and hence also on the nature of theresponse signal generated by the sense unit 322), the device 310 mayalso include a peak detection circuit 326 a which in this embodimentalso serves as a sample/hold buffer, and an associated reset circuit 326b operable to reset the peak detector. In most practical applicationsthe device 310 will also include a multiplexer between the signalgenerator 320 and the touch panel 312, so as to have the capability ofaddressing any one of a plurality of drive electrodes at a given time,as well as a multiplexer between the sense unit 322 (or between theoptional circuit 326 b) and the ADC unit 324, to allow a single ADC unitto rapidly sample the amplitudes associated with multiple receiveelectrodes, thus avoiding the expense of requiring one ADC unit for eachreceive electrode.

The drive unit 320 preferably is or includes a voltage source with aninternal impedance that is preferably low enough to maintain good signalintegrity, reduce injected noise, and/or maintain fast signal rise andfall times. The drive unit 320 provides a time-varying drive signal atan output thereof to the drive electrode 314. The drive signal mayconsist essentially of a single, isolated pulse, or it may comprise aplurality of such pulses or a train of pulses that form a continuous ACwaveform, or waveform packet, such as a sinusoidal wave, a square wave,a triangle wave, and so forth. In this regard, the term “pulse” is usedin a broad sense to refer to a distinctive signal variation and is notlimited to a rectangular shape of short duration and high amplitude. Ifrapid detection of touch(es) on the touch panel is desired, the drivesignal preferably includes only the smallest number of pulses necessaryto obtain a reliable measurement of the coupling capacitance at a givennode. This becomes particularly important for touch panels that havelarge electrode matrices, i.e., a large number of nodes to sense. Thepeak or maximum amplitude of the drive pulse(s) is preferably relativelyhigh, e.g., from 3 to 20 volts, to provide good signal-to-noise ratios.Though shown in FIG. 3a as driving electrode 314 from only one end, insome embodiments drive unit 320 may be configured to drive electrode 314from both of its ends. This may be useful, for example, when electrode314 has high resistance (thus increased drive signal attenuation andsusceptibility to noise contamination), as may exist on large ITO-basedmatrix-type touch sensors.

The reader should keep in mind that there may be a distinction betweenthe drive signal provided at the output of drive unit 320, and the drivesignal being delivered to a particular drive electrode 314. Thedistinction becomes important when, for example, a multiplexer or otherswitching device is placed between the drive unit 320 and the touchpanel 312 in order to selectively couple the drive unit to a pluralityof drive electrodes, e.g., one at a time. In such a case, the drive unit320 may have at its output a continuous AC waveform, such as squarewave, triangle wave, or the like, yet by virtue of the switching actionof the multiplexer, only one pulse of such a waveform, or only a fewpulses, may be delivered to any given drive electrode at a time. Forexample, one pulse of a continuous AC waveform may be delivered to afirst drive electrode, the next pulse of the AC waveform may bedelivered to the next drive electrode, and so on until all driveelectrodes have been driven, whereupon the next pulse of the AC waveformis delivered again to the first drive electrode and so forth in arepeating cycle.

As will be explained further below in connection with FIGS. 4-6, theshape of the pulses used in the drive signal may have an impact on thechoice of detection/measurement electronics to be used in the device.Examples of useable pulse shapes include rectangle pulses, ramped pulses(whether symmetric or asymmetric), and sine wave (e.g., bell-shaped)pulses.

The drive unit 320 may if desired be programmable to provide differentpulses at different times. For example, if the drive unit is coupled toa plurality of drive electrodes through a multiplexer, the drive unitmay be programmed to provide different signal levels for different driveelectrodes to compensate for electrode-to-electrode variations in lineresistance and stray capacitance. For example, a drive electrodedisposed at a position that requires a long conduction length throughthe receive electrode(s) is beneficially driven with a higher amplitudedrive signal than a drive electrode disposed at a position that requiresa shorter conduction length, so as to compensate for losses associatedwith the receive electrodes. (For example, referring to the electrodematrix of FIG. 1, if row electrodes 118 a-e are the drive electrodes,then a drive signal on electrode 118 a is coupled through longer lengthsof the receive electrodes 116 a-e than a drive signal on electrode 118 edue to the placement of the control lines 126 proximate electrode 118e.) Providing different drive signal levels for different driveelectrodes in this way is particularly advantageous for large electrodematrices, because rather than programming a large number of detectioncircuits (corresponding to the number of receive electrodes) for lossesin the touch screen, only one drive signal is adjusted by a selectedamount, with drive signals delivered to different drive electrodes beingadjusted by differing amounts as appropriate.

The drive signal provided to the drive electrode 314 is capacitivelycoupled to receive electrode 316 via the coupling capacitance C_(c), thereceive electrode in turn being connected to sense unit 322. The senseunit 322 thus receives at an input thereof 322 a the drive signal (astransmitted by the electrodes 314, 316 and coupling capacitance C_(c)),and generates therefrom a response signal at an output 322 b.Preferably, the sense unit is designed so that the response signalincludes a differentiated representation of the drive signal, anamplitude of which is responsive to the coupling capacitance C_(c). Thatis, the response signal generated by the sense unit preferably includesin some form at least an approximation of the derivative with respect totime of the drive signal. For example, the response signal may includethe time derivative of the drive signal, or a version of such signalthat is inverted, amplified (including amplification less than 1),offset in voltage or amplitude, and/or offset in time, for example. Torepeat from the earlier discussion, if the drive signal delivered to thedrive electrode is represented by a function f(t), then the responsesignal may be or comprise, at least approximately, a function g(t),where g(t)=d f(t)/dt.

An exemplary circuit to perform such function is shown in FIG. 3a . Theinput to such circuit, shown at 322 a, is the inverting input (−) of anoperational amplifier 322 c. The other input of the op amp, anon-inverting input (+), is set to a common reference level that can beoptimized for maximum signal range. In FIG. 3, this reference level isshown as ground potential for simplicity, but non-zero offset voltagescan also be used. A feedback resistor 322 d is connected between theoutput of the op amp at 322 b and the inverting input. When connected inthis way, the inverting input of the op amp 322 c, i.e., the input 322a, is maintained as a virtual ground summing point, and no signal isobserved at that point. This also means that the receive electrode 316is maintained at a constant voltage substantially equal to the voltageat which the non-inverting input of the op amp is held. The feedbackresistor 322 d can be selected to maximize signal level while keepingsignal distortion low, and can be otherwise set or adjusted as describedherein.

The op amp 322 c connected in this fashion, in combination with thecoupling capacitance C_(c), has the effect of producing a differentiatedrepresentation of the drive signal that is delivered to drive electrode314. In particular, the current I flowing through the feedback resistor322 d at any given time is given by:I≈C _(c) *dV/dt,where C_(c) is the coupling capacitance, V represents the time-varyingdrive signal delivered to the drive electrode, and dV/dt is thederivative with respect to time of V. Although this equation isnominally correct, the reader will understand that it does not take intoaccount various second order effects caused by, for example, parasiticresistance and capacitance of the electrodes being used, op ampcharacteristics and limitations, and the like, which can affect both themagnitude and the dynamic response of the current I. Nevertheless, thecurrent I, flowing through the feedback resistor, produces a voltagesignal at the output 322 b which corresponds to the response signaldiscussed above. Due to the direction of current flow through thefeedback resistor, this response signal is inverted insofar as apositive dV/dt (V increases with time) produces a negative voltage atoutput 322 b, and a negative dV/dt (V decreases with time) produces apositive voltage at output 322 b, with specific examples given below inconnection with FIGS. 4-6. This can be expressed as:V _(RS) ≈−R _(f) *C _(c) *dV/dt,where V_(RS) represents the response signal voltage at the output 322 bat any given time, and R_(f) is the resistance of feedback resistor 322d. Note that the amplitude (voltage) of the response signal is nominallyproportional to the coupling capacitance C_(c). Thus, since a touch atthe node of the electrodes 314, 318 reduces the coupling capacitanceC_(c), a measure of the peak amplitude or other characteristic amplitudeof the response signal provided by sense unit 322 can be analyzed todetermine the presence of a touch at that node.

In embodiments in which receive electrode 316 is one of a plurality ofreceive electrodes, it may be desirable to include a dedicated senseunit 322 for each receive electrode. Further, it may be advantageous toprovide different amounts of amplification (e.g., different feedbackresistor values for the different op amps) for the different sense unitsto compensate for signal losses in the touch screen that are differentfor different drive electrodes. For example, a receive electrodedisposed at a position that requires a long conduction length throughthe drive electrode(s) is beneficially provided with a greateramplification than a receive electrode disposed at a position thatrequires a shorter conduction length, so as to compensate for lossesassociated with the drive electrodes. (For example, referring to theelectrode matrix of FIG. 1, if row electrodes 116 a-e are the receiveelectrodes, then a signal received from electrode 116 a is coupledthrough longer lengths of the drive electrodes 118 a-e than a signalreceived from electrode 116 e due to the placement of the control lines128 proximate electrode 116 e.) Providing different amounts ofamplification for different receive electrodes in this way isparticularly advantageous for large electrode matrices, because it canreduce the need to program a large number of detection circuits(corresponding to the number of receive electrodes) for losses in thetouch screen.

As mentioned above, device 310 may also include peak detection circuit326 a which in this embodiment also serves as a sample/hold buffer, andan associated reset circuit 326 b operable to reset the peak detector.These circuit elements can be used in cases where the peak amplitude ofthe response signal generated by the sense unit 322 is to be used as ameasure of the coupling capacitance C_(c). Such cases can includeembodiments in which the response signal provided by the sense unit 322is highly transient, e.g., in cases where one or more rectangle pulsesare used for the drive signal (see e.g. FIG. 4a below). In such cases,the peak detector 326 a operates to maintain the peak amplitude of theresponse signal for a relatively long time to allow reliable samplingand conversion to a digital value by the ADC 324. In embodiments havinga plurality of receive electrodes, a single ADC may be cyclicallycoupled to the detection circuitry of each receive electrode, requiringeach detection circuit to maintain the measurement voltage for anextended period of time. After the measurement is made by the ADC 324,the peak detector can be reset by operation of reset circuit 326 b sothat a new peak value can be measured in a subsequent cycle.

The basic operation of the diode/capacitor combination depicted for peakdetector 326 a, including its ability to maintain the peak voltage foran extended period without discharging the capacitor through the senseunit 322, will be apparent to the person of ordinary skill in the art,with no further explanation being necessary. Likewise, the basicoperation of the reset circuit 326 b, responding to a suitable resetcontrol signal provided at contact 326 c, will be apparent to the personof ordinary skill in the art. Note that other known electronic devicescapable of carrying out one or more functions of the described senseunit, peak detector, sample/hold buffer, and/or reset circuit, whetherin hardware, software, or combinations thereof, are fully contemplatedherein.

As mentioned previously, the ADC 324 is preferably provided to convertthe amplitude value associated with the response signal to a digitalformat for use with digital components such as a microprocessor forfurther processing. The ADC may be of any suitable design, e.g., it maycomprise a high speed successive approximation register (SAR) and/or asigma-delta type converter.

With regard to further processing of the measured amplitude value of agiven node, the measured amplitude value can be stored in a memoryregister. If desired, multiple such values associated with the givennode may be stored and averaged, e.g. for noise reduction purposes.Furthermore, the measured amplitude value is preferably compared to areference value in order to determine if a reduction of the couplingcapacitance has occurred, i.e., if some amount of touch is present atthe given node. Such comparison may involve subtraction of the measuredvalue from the reference value, for example. In embodiments involving alarge touch matrix containing many nodes, the measured values for all ofthe nodes can be stored in memory, and individually compared torespective reference values in order to determine if some amount oftouch is present at each node. By analyzing the comparison data, thepositions of multiple temporally overlapping touches, if present on thetouch surface, can be determined. The number of temporally overlappingtouches capable of being detected may be limited only by the dimensionsof the electrode grid in the touch panel and the speed of thedrive/detection circuitry. In exemplary embodiments, interpolation isperformed for differences detected for neighboring nodes so as toaccurately determine a touch location lying between nodes.

FIG. 3b depicts touch device 348 which is similar to touch device 310shown in FIG. 3a , except that it includes voltage source 349 as aninput to the differentiating amplifier that is part of sense unit 322.This voltage input may be configured as needed to bring circuit outputinto a sensing range for the ADC. For example, some ADCs have sensingranges from 0.5V to +3V. The peak of the sense unit 322 output signalshould be within this range to digitize the voltage accurately. Voltagesource 349 (or gain, in the context of sense unit 322) can be fixed atone voltage for all receiver electrodes, or it can be adjusted forparticular receive electrodes. In some embodiments, differing voltagesare provided to sense units in groups of 4-10 receive electrodes using aresistor ladder network. In some embodiments, gain is set to compensatefor signal drop off due to resistance on the driven electrodes.

FIG. 3c depicts touch device 350 which is similar to touch device 310shown in FIG. 3a , but containing additional circuitry that in someembodiments may better accommodate noise from displays such as LCDdisplays. LCD addressing frequencies are generally near or overlappingthe frequencies used by controller 114 to interface with touch panel112. This results in noise on the receiver electrodes which may show upas a common mode signal. A differential amplifier may be used toeliminate this common mode signal. The circuit shown in FIG. 3c adds adifferential amplifier 352 and additional peak detection circuit 351(configured to detect peaks of negative voltage), and an additionalreset circuit 353.

FIG. 3d depicts touch device 362 which is similar to touch device 310shown in FIG. 3a , but containing additional circuitry that in someembodiments may better accommodate noise from displays such as LCDdisplays, and more particularly LCD displays employing in-planeswitching technology, which improves display viewing angle butintroduces certain noise artifacts into an adjacently disposed touchsensor. The noise artifacts may be characterized by electromagneticinterference in the same frequency band as the pulses and signalsapplied to the drive electrode. FIG. 3d adds a resistor after sense unit322, but before the capacitor that is shown as included in peakdetection circuit 326 a. The resistor is shown implemented after thediode in peak detection circuit 326 a, but it may also be implementedbefore the diode. This resistor limits the charging effect in peakdetection circuit 326 a from any pulse or signal applied to a driveelectrode. Thus an increased number of pulses may be used in ameasurement cycle (for example, 8 pulses rather than 3), which reducesthe impact of some portion of those pulses being contaminated bypositive noise pulses, or produced by positive anomalous noise. Ofcourse, an increased number of pulses may be used in an embodiment suchas 3 a that does not contain the additional resistor of FIG. 3d and withit a relatively larger capacitor used in peak detection circuit 326 a.However, the peak detection circuit 326 a is discharged after eachsample cycle, and the discharge time is commensurate with the amount ofcharge held by the capacitor. The additional resistor of FIG. 3d allowsfor a smaller charge accumulated in the capacitor of peak detectioncircuit 326 a, which allows for faster discharge time.

FIG. 3e depicts touch device 360, which is similar to touch device 310shown in FIG. 3a , but containing additional circuitry that in someembodiments may better accommodate touch panel having electrodes withlower resistance. Such touch panels may have electrodes comprised ofcopper, gold, silver, or other metallic micro-wires, and have resistancelevels of <10K ohms. To accommodate lower resistance electrodes, touchdevice 360 adds the resistor and capacitor depicted in low impedancestability circuit 361. This additional circuitry stabilizes amplifier322 c's loop gain by adding 45 degrees of phase margin at the amplifierunity loop gain crossover frequency.

Any of the embodiments shown in FIG. 3a through 3e could be embodied in,for example, an application specific integrated circuit (ASIC).

Turning now to FIG. 4a , we see there a voltage vs. time graph of aparticular drive signal 410 and a corresponding voltage vs. time graphof a (modeled) response signal 412 generated by a sense unit of the typedepicted in FIG. 3a . For purposes of the model, the electroniccharacteristics of the drive electrode, receive electrode, and couplingcapacitance (including the effect of a touch thereon, i.e., decreasingthe capacitance from 2.0 pf to 1.5 pf) were assumed to be as describedabove in connection with the representative embodiment of FIG. 3a .Furthermore, the feedback resistor 322 d for the op amp 322 c wasassumed to be on the order of 2 M ohms.

The drive signal 410 is seen to be a square wave, containing a series ofrectangle pulses 411 a, 411 c, 411 e, . . . 411 k. This entire signalwas assumed to be delivered to a particular drive electrode, although inmany embodiments a smaller number of pulses, e.g. only one or two, maybe delivered to a given drive electrode at a given time, after which oneor more pulses may be delivered to a different drive electrode, and soon. The response signal 412 generated by the sense unit is seen tocomprise a plurality of impulse pulses 413 a-l, two for each rectanglepulse 411 a, as one would expect for a differentiated square wave. Thus,for example, the drive pulse 411 a yields a negative-going impulse pulse413 a associated with the positive-going transition (left side) of therectangle pulse, and a positive-going impulse pulse 413 b associatedwith the negative-going transition (right side) of the rectangle pulse.The impulse pulses are rounded as a result of the op amp signalbandwidth and the RC filter effects of the touch screen. Despite thesedeviations from an ideal derivative with respect to time of signal 410,the response signal 412 can be considered to comprise a differentiatedrepresentation of the drive signal.

As shown, the drive pulses 411 a, 411 c, 411 e, . . . 411 k, all havethe same amplitude, although pulses of differing amplitude can also bedelivered as explained above. However, despite the common amplitude ofthe drive pulses, the impulse pulses 413 a-g occurring in the timeperiod 412 a are seen to have a first peak amplitude, and impulse pulses413 h-l occurring in the time period 412 b are seen to have a secondpeak amplitude less than the first peak amplitude. This is because themodel introduced a change in coupling capacitance C_(c) at a point intime after impulse pulse 413 g and before impulse pulse 413 h, thechange corresponding to a transition from a non-touch condition (C_(c)=2pf) to a touch condition (C_(c)=1.5 pf). The reduced peak amplitude ofthe impulse pulses during time period 412 b can be readily measured andassociated with a touch event at the applicable node.

The transient nature of the impulse pulses 413 a-l make themparticularly suited for use with a peak detector and sample/hold bufferas described in connection with FIG. 3, so that an accurate measurementof the peak amplitude can be obtained and sampled by the ADC.

FIG. 4b depicts graphs showing representative waveforms from anembodiment that includes sequential driving of driven electrodes.Waveforms 430, 431, and 432 are representative of pulsed signals duringa period of time, t, on three separate (possibly adjacent one another)driven electrodes (a first, second, and third row on a matrix-typesensor, for example). Waveforms 433, 434, and 435 are representative ofdifferentiated output resulting from the pulsed signals on threeseparate receive electrodes (columns on a matrix-type sensor, forexample) during the same time period. Note that each receive electrode(column) has a similar response profile. The driven electrodescorresponding to waveforms 432, 431, and 431 are driven sequentially.After each an electrode is driven (represented by any individual ones ofwaveforms 430, 431, or 432), a voltage representative of peak amplitudewill be available in the peak detect circuit associated with eachreceive electrode (column) as described above in connection with FIG. 3.Thus, after each driven electrode is driven (row), the resultant voltageon the peak detect circuit for all receive electrodes (columns) issampled, then the associated peak detect circuit reset, then the nextsequential driven electrode is driven (and so on). In this way, eachnode in the matrix-type capacitive touch sensor can be individuallyaddressed and sampled.

FIG. 5a depicts a pair of graphs similar to those of FIG. 4a , and forthe same electronic configuration of drive electrode, receive electrode,coupling capacitance, and sense unit, but for a different drive signalshape. The drive signal 510 of FIG. 5a includes ramped pulses 511 a, 511c, 511 e, . . . 511 i, so that the resultant response signal 512includes rectangle pulses 513 a-j. The rectangle pulses predicted by themodel exhibited near-vertical hi/lo transitions with slightly roundedcorners, which have been redrawn as vertical lines and sharp corners forsimplicity. The rise and fall times of the rectangle pulses are limitedby the RC transmission line in the drive and receive electrodes beingused. The drive pulses 511 a, etc. are characterized by a symmetricalramp shape, with the first half of each pulse having a positive-goingslope and the second half having a negative-going slope of the samemagnitude. This symmetry is also then carried over to the responsesignal 512, where negative-going pulses 513 a, 513 c, and so forth aresubstantially balanced by positive-going pulses 513 b, 513 d, and so on.Similar to the description of FIG. 4a , the model introduces a change incoupling capacitance C_(c) at a point in time after rectangle pulse 513e and before rectangle pulse 513 f, i.e., in the transition from timeperiod 512 a to time period 512 b, the change corresponding to atransition from a non-touch condition (C_(c)=2 pf) to a touch condition(C_(c)=1.5 pf). The reduced amplitude of the response signal pulsesoccurring during time period 412 b can be readily measured andassociated with a touch event at the applicable node. A feature of FIG.5a worth noting is the relatively steady-state characteristic (over thetime scale of given pulse) of the response signal 512 at each plateau ofeach pulse 513 a-j, where the “plateau” of a negative-going pulse 513 a,513 c, and so on is understood to be the “bottom” of the pulse shaperather than the “top” as with pulses 513 b, d, and so forth. Thissteady-state characteristic is a consequence of the drive pulses havinga constant slope over a substantial portion of the drive pulses, i.e., aramped shape. In some embodiments, the touch device designer may wish totake advantage of this steady-state characteristic so as to eliminateunnecessary circuit items and reduce cost. In particular, since theresponse signal itself maintains a substantially constant amplitude (theplateau of a pulse) over the time scale of the pulse, and since thisconstant amplitude is indicative of or responsive to the couplingcapacitance C_(c), the peak detector, sample/hold buffer, and resetcircuit described in connection with FIG. 3a may no longer be necessaryand may be eliminated from the system, provided the time scale of thesteady-state characteristic is long enough for the ADC to sample andmeasure the amplitude. If desired, for noise-reduction, the responsesignal generated by the sense unit in such cases can be sent through alow-pass filter whose cutoff frequency is selected to substantiallymaintain the same overall fidelity or shape as the unfiltered pulseswhile filtering out higher frequency noise. The output of such a filter,i.e., the filtered response signal, may then be supplied to the ADC. Ofcourse, in some cases it may be desirable to keep the peak detector,sample/hold buffer, and reset circuit, whether or not the low-passfilter is utilized, for ramp-type drive pulses.

If desired, a rectifying circuit can be used in touch device embodimentsthat produce positive- and negative-going pulses in the response signal,see e.g. signal 412 of FIG. 4a and signal 512 of FIG. 5a . Therectification of these signals may have corresponding benefits for othercircuit functions, such as peak detection and analog-to-digitalconversion. In the case of signal 512 of FIG. 5a , a rectified versionof that signal advantageously maintains a steady-state voltage levelsubstantially continuously (ignoring transient effects due to op amplimitations and RC transmission line effects) as a result of thesymmetry of the respective signals.

FIG. 5b depicts pairs of graphs showing representative waveforms fromembodiments that include sequential driving of driven electrodes,similar to FIG. 4b , except using a different type of driven waveform.Waveforms 760, 761, and 762 are representative driven triangle pulsesignals during a time period, t, on three separate (possibly adjacentone another) driven electrodes (a first, second, and third row on amatrix-type sensor, for example). Waveforms 763, 764, and 765 arerespective resultant waveforms as would be seen on receive electrodes(for example, columns) during the same time period.

Turning now to FIG. 6a , the pair of graphs there are similar to thoseof FIGS. 5a and 4a , and assume the same electronic configuration ofdrive electrode, receive electrode, coupling capacitance, and senseunit, but a yet another drive signal shape is used. The drive signal 610of FIG. 6b includes ramped pulses 611 a-e, which yield the resultantresponse signal 612 having substantially rectangle pulses 613 a-e.Unlike the symmetrical ramp shapes of FIG. 5a , ramped pulses 611 a-eare asymmetrical so as to maximize the fraction of the pulse time usedby the ramp. This ramp maximization, however, results in a rapidlow-to-high transition on one side of each drive pulse, which produces anegative-going impulse pulse bounding each rectangle pulse of theresponse signal 612. In spite of the resulting deviations from perfectrectangularity, the pulses 613 a-e are nevertheless substantiallyrectangular, insofar as they maintain a relatively constant amplitudeplateau between two relatively steep high-to-low transitions. As such,and in a fashion analogous to signal 512 of FIG. 5a , the pulses ofsignal 612 include a steady-state characteristic as a consequence of thedrive pulses having a constant slope over a substantial portion of thedrive pulses, i.e., a ramped shape. The touch device designer may thusagain wish to take advantage of this steady-state characteristic byeliminating the peak detector, sample/hold buffer, and reset circuit,provided the time scale of the steady-state characteristic is longenough for the ADC to sample and measure the amplitude. A low-passfilter may also be added to the circuit design as described above.

FIG. 6b depicts a pair of graphs showing representative waveforms fromembodiments that include sequential driving of driven electrodes,similar to FIG. 4b and FIG. 5b , except using a different type of drivenwaveform. Waveforms 750, 751, and 752 are representative driven rampedpulse signals during a time period, t, on three separate (possiblyadjacent one another) driven electrodes (a first, second, and third rowon a matrix-type sensor, for example). Waveforms 753, 754, and 755 (FIG.7b ) and 763, 764, and 765 (FIG. 7c ) are respective resultant waveformsas would be seen on receive electrodes (for example, columns) during thesame time period.

Turning now to FIG. 7, we see there a voltage vs. time graph of a pulseddrive signal 807 and a corresponding voltage vs. time graph of a(modeled) first response signal 801 and second response signal 802 aswould be output generated by sense unit 322 and differential amplifier352, respectively, of the circuit depicted in FIG. 3c . For purposes ofthe model, the electronic characteristics of the drive electrode,receive electrode, and coupling capacitance (including the effect of atouch thereon, i.e., decreasing the capacitance from 2.0 pf to 1.5 pf)were assumed to be as described above in connection with therepresentative embodiment of FIG. 3 a.

First response signal 801 is the modeled output from sense unit 322. Itincludes a sinusoidal form indicative of a common mode signal similar tothat which might be received as noise from an LCD panel. Response signal802 is the respective modeled output from differential amplifier 352(shown for the purposes of illustration as a short-dashed line; theactual output would be a solid line). The output from differentialamplifier 352 is in effect the sum of the pulses (shown not to scale forillustrative purposes). The individual pulses on FIG. 7 (803 a . . . d,804 e, f, g) have the same profile as pulses 413 a . . . k in FIG. 4a ,but they appear differently in FIG. 7 due to scaling. The first negativepulse (803 a) is peak detected and summed on the inverting input of theamplifier giving the first step on response signal 802 (step 805 a). Thepositive pulse (804 e) is then peak detected and summed on thenon-inverting input on the amplifier, giving the sum of both thepositive and negative peaks at the output (step 805 b). Neithersucceeding pulses nor the common mode signal substantially effect thevoltage level of response signal 802 after step 805 b. A touch may besensed by measuring a first voltage sample represented by waveform 802after a series of pulses (that is, after the voltage has reached aplateau defined by step 805 b), resetting peak detectors using resetcircuits 353 and 326 b (FIG. 3c ), and then measuring a second voltagesample using the same or a similar process, and so forth. In certainembodiments, changes to these sample voltages, relative to somethreshold, are indicative of a touch.

FIG. 8 is a schematic view of a touch device 710 that includes a touchpanel 712 having a 4×8 matrix of capacitively coupled electrodes, andvarious circuit components that can be used to detect multiplesimultaneous touches on the touch panel. The electrode matrix includes atop electrode array comprising parallel drive electrodes a, b, c, and d.Also included is a lower array comprising parallel receive electrodesE1, E2, E3, E4, E5, E6, E7, and E8. The top electrode array and thelower electrode array are arranged to be orthogonal to one another. Thecapacitive coupling between each pair of orthogonal electrodes, referredto above for a given node as the coupling capacitance C_(c), is labeledfor the various nodes of the matrix as C1 a, C2 a, C3 a, C4 a, C1 b, C2b, and C3 b, etc., through C8 d as shown, the values of which may all beapproximately equal in an untouched state but which decrease when atouch is applied as described previously. Also depicted in the figure isthe capacitance between the various receive electrodes and ground(C1-C8) and between the various drive electrodes and ground (a′ throughd′).

The 32 nodes of this matrix, i.e., the mutual capacitances or couplingcapacitances associated therewith, are monitored by circuitry asdescribed with respect to FIG. 3a : drive unit 714; multiplexer 716;sense units S1-S8; optional peak detectors P1-P8, which may alsofunction as sample/hold buffers; multiplexer 718; as well as ADC 720;and controller 722, all connected as shown with suitable conductivetraces or wires (except that connections between controller 722 and eachof the peak detectors P1-P7 are omitted from the drawing for ease ofillustration).

In operation, controller 722 causes drive unit 714 to generate a drivesignal comprising one or more drive pulses, which are delivered to driveelectrode a by operation of multiplexer 716. The drive signal couples toeach of receive electrodes E1-E8 via their respective mutualcapacitances with drive electrode a. The coupled signal causes the senseunits S1-S8 to simultaneously, or substantially simultaneously, generateresponse signals for each of the receive electrodes. Thus, at this pointin time in the operation of device 710, the drive signal being deliveredto drive electrode a (which may include, for example, a maximum of 5, 4,3, or 2 drive pulses, or may have only one drive pulse) is causing senseunit S1 to generate a response signal whose amplitude is indicative ofcoupling capacitance C1 a for the node E1/a, and sense unit S2 togenerate a response signal whose amplitude is indicative of couplingcapacitance C2 a for the node E2/a, etc., and so on for the other senseunits S3-S8 corresponding to nodes E3/a through E8/a, all at the sametime. If the response signals are of a highly transient nature, e.g. aswith signal 412 of FIG. 4a , then peak detectors P1-P8 may be providedto detect the peak amplitudes of the respective response signalsprovided by sense units S1-S8, and optionally to sample and hold thoseamplitudes at the outputs thereof which are provided to the multiplexer718. Alternatively, if the response signals have a significantsteady-state characteristic, e.g. if they are in the form of one or morerectangle pulses as with signals 512 and 612 described above, then thepeak detectors may be replaced with low-pass filters, or the peakdetectors may simply be omitted so that the outputs of the sense unitsfeed directly into the multiplexer 718. In either case, while thecharacteristic amplitude signals (e.g. peak amplitude or averageamplitude of the response signals) are being delivered to themultiplexer 718, the controller 722 rapidly cycles the multiplexer 718so that the ADC 720 first couples to peak detector P1 (if present, or toa low-pass filter, or to S1, for example) to measure the characteristicamplitude associated with node E1/a, then couples to peak detector P2 tomeasure the characteristic amplitude associated with node E2/a, and soforth, lastly coupling to peak detector P8 to measure the characteristicamplitude associated with node E8/a. As these characteristic amplitudesare measured, the values are stored in the controller 722. If the peakdetectors include sample/hold buffers, the controller resets them afterthe measurements are made.

In the next phase of operation, the controller 722 cycles themultiplexer 714 to couple the drive unit 714 to drive electrode b, andcauses the drive unit to generate another drive signal that againcomprises one or more drive pulses, now delivered to electrode b. Thedrive signal delivered to electrode b may be the same or different fromthat delivered previously to electrode a. For example, for reasonsrelating to touch panel losses explained above, the drive signaldelivered to electrode b may have a smaller amplitude than thatdelivered to electrode a, due to electrode b's closer proximity to theends of sense electrodes E1-E8 from which the response signals arederived (and thus lower losses). In any case, the drive signal deliveredto electrode b causes sense unit S1 to generate a response signal whoseamplitude is indicative of coupling capacitance C1 b for the node E1/b,and sense unit S2 to generate a response signal whose amplitude isindicative of coupling capacitance C2 b for the node E2/b, etc., and soon for the other sense units S3-S8 corresponding to nodes E3/b throughE8/b, all at the same time. The presence or absence of peak detectorsP1-P8, or of sample/hold buffers, or of low-pass filters discussed abovein connection with the first phase of operation is equally applicablehere. In any case, while the characteristic amplitude signals (e.g. peakamplitude or average amplitude of the response signals) are beingdelivered to the multiplexer 718, the controller 722 rapidly cycles themultiplexer 718 so that the ADC 720 first couples to peak detector P1(if present, or to a low-pass filter, or to S1, for example) to measurethe characteristic amplitude associated with node E1/b, then couples topeak detector P2 to measure the characteristic amplitude associated withnode E2/b, and so forth, lastly coupling to peak detector P8 to measurethe characteristic amplitude associated with node E8/b. As thesecharacteristic amplitudes are measured, the values are stored in thecontroller 722. If the peak detectors include sample/hold buffers, thecontroller resets them after the measurements are made.

Two more phases of operation then follow in similar fashion, wherein adrive signal is delivered to electrode c and the characteristicamplitudes associated with nodes E1/c through E8/c, are measured andstored, and then a drive signal is delivered to electrode d and thecharacteristic amplitudes associated with nodes E1/d through E8/d, aremeasured and stored.

At this point, characteristic amplitudes of all of the nodes of thetouch matrix have been measured and stored within a very shorttimeframe, e.g., in some cases less than 20 msec or less than 10 msec,for example. The controller 722 may then compare these amplitudes withreference amplitudes for each of the nodes to obtain comparison values(e.g., difference values) for each node. If the reference amplitudes arerepresentative of a non-touch condition, then a difference value of zerofor a given node is indicative of “no touch” occurring at such node. Onthe other hand, a significant difference value is representative of atouch (which may include a partial touch) at the node. The controller722 may employ interpolation techniques in the event that neighboringnodes exhibit significant difference values, as mentioned above.

Stylus Support

The embodiments described above support the resolution of multipletemporally overlapping touches, as with a finger or other pointingdevice that interferes with the coupling capacitance at a node in atouch panel. The electronics described above with respect particularlyto FIGS. 3a through 3e , or associated firmware, may be adapted,however, to support the resolution of stylus contact, or in someembodiments near contacts, made to the touch sensitive device (such as atouch panel). The remainder of this detailed description describesapproaches to integrating stylus support to the earlier describedelectronics.

Any instrument that sufficiently interferes with the capacitive couplingat a node in the touch panel may be used as stylus with theabove-described electronics. Some aftermarket products are currentlyavailable that provide, at the tip of a pen or pointing device, aconductive material that couples with transparent electrodes in a touchsensitive device in a manner not unlike that of a finger. These devicesare generally passive devices, and may not have the resolution necessaryto support, for example, high resolution signatures.

One embodiment of an active stylus is shown in FIG. 9. Stylus 910includes a housing 915, which could be metal or plastic, designed to becomfortably held by a user, and shaped in one embodiment like a pen. Oneor more communication lines 920 tether the stylus to a host controllerand are used for communication between the stylus microprocessor, aswell as to provide power. Microprocessor 901 is programmed tocommunicate via communication lines 920 with a host controller, such ascontroller 114 (FIG. 1). Accelerometer 904 is shown communicativelycoupled to microprocessor 901. Accelerometer 904 provides informationabout the orientation of the stylus relative to the touch panel, thenthe information used in conjunction with known interpolation techniquesto provide increased accuracy of contact points. Tip force sensor 905 isshown communicatively coupled to microprocessor 901. Tip force sensor905 provides information indicative of the pressure being applied to thetip of the stylus. Such a tip force sensor could be associated withturning the stylus on, putting the stylus into an active mode, or itcould be used in applications where the pressure applied may beassociated with particular modalities of input (for example, in writingthe use of pressure may be reported to an application which thenassociates input with a bold typeface). Various buttons (906) may beemployed to provide a user with various functionalities, such as turningthe stylus on or off. Tip electronics 907, as further described withrespect to the following three stylus embodiments, may include stylusdrive electronics that provide a signal into the touch panel (and whichwould include a drive unit and a drive electrode), stylus receiveelectronics that receive a signal from the driven touch panel electrodes(and which would include stylus receive electronics and a receiveelectrode). In one embodiment described below, the stylus tipelectronics 907 are configured to alternatively drive, and then receive,capacitively coupled signals on a common electrode (and thus wouldinclude both a stylus drive unit and stylus receive electronics). Insome embodiments, particular elements shown within stylus housing 915may be subsumed by functionality provided by a host controller. Forexample, the host controller 114 may be configured to interact with thevarious components described with respect to the stylus viacommunication lines 920, which could render microprocessor 901unnecessary.

More specifically the microprocessor in one embodiment is based on aCortex ARM microprocessor, the architecture for which is available fromARM, Inc. of San Jose, Calif., and the accelerometer is a three-axissensitive device similar to units commercially available from AnalogDevices of Boston, Mass., or ST Microelectronics of Geneva, Switzerland.

Stylus as Drive Electrode and Receive Electrode

In one embodiment the stylus may be integrated with theearlier-described multi-touch sensitive systems by configuring thestylus tip electronics 907 with both a stylus drive unit and stylusreceive electronics. The stylus drive unit, which is similar to or thesame as the drive unit or signal generator described earlier withrespect to at least FIG. 1, is configured to generate a drive signal anddeliver the drive signal to the stylus electrode. The stylus receiveelectronics may be configured similar to any of the embodiments shownwith respect to FIGS. 3a through 3e , and may includes a stylus senseunit (similar in one embodiment to or the same as sense unit 322 in FIG.3a ). Depending on the implementation, stylus receive electronics mayalso include a stylus peak detection circuit (similar to or the same aspeak detection circuit 326 a in FIG. 3a ).

FIG. 10 depicts tip electronics 907 that include both a stylus driveunit and the stylus receive electronics. Pen tip 1014 is in oneembodiment located proximate the part of the stylus designed to be incontact with or near contact with the touch pane, to be used forpointing. Pen tip 1014 includes the stylus electrode, which may bealternatively operated in driven or receive mode, depending on switch1010, which may be controlled by microprocessor 901. When in stylusdrive mode, stylus drive unit 1012 provides a stylus drive signal to thestylus electrode, which may comprise one or more square waves, trianglewaves, ramped waves, or the like. If the stylus electrode issufficiently close to the touch panel, as would be the case when a useris using the stylus to interact with the touch panel and the stylus isin contact with the touch panel, the stylus drive signal capacitivelycouples to a receive electrode in the touch panel 112. In this way, thestylus electrode, when in drive mode, acts in effect like an additionaldriven electrode of touch panel 112, and the firmware running oncontroller 114 is programmed to sequentially drive the drive rows, andthen command the stylus drive unit to drive the stylus electrode. Asdescribed above with respect to embodiments shown in FIGS. 3a through 3e, for each drive sequence of a driven electrode (including the drivenelectrodes in touch pane 112 and the stylus electrode when in drivemode), the receive electrodes simultaneously receive. Controller 114 isthus programmed to accommodate a stylus drive cycle whereby, aftertouches to touch panel 112 have been resolved as described above, thestylus electrode is driven and the receive electrodes in touch panel 112that are proximate the stylus electrode receive a signal that is thecoupling capacitance (C_(c)) between the stylus drive electrode and thetouch panel receive electrodes. Embodiments described above with respectto FIGS. 3a through 3e show various approaches to determining therelative C_(c) of the receive electronics, each of which could be used,possibly in conjunction with known interpolation techniques, to revealthe position of the stylus on the receive electrode.

To resolve the location of the stylus tip relative to the other, yetunresolved axis, stylus tip electronics 907 is switched (via switch1010) into stylus receive mode. The driven electrodes of touch panel 112are sequentially driven, and a C_(c) arises between particular drivenelectrodes and the stylus electrode, which is sensed by sense unit 3322and peak detected via stylus peak detect unit 3326 a, sampled via ADC3324 a, then reset via stylus reset circuit 3326 b (all in a mannersimilar to the embodiment shown with respect to FIG. 3a ). The stylusreceive electronics, when in stylus receive mode, effectively act as anadditional receive electrode, and controller 114 is programmed to querysurrogates of C_(c) for each of the receive electrodes as well as thestylus receive electrodes, after each drive sequence associated with adriven electrode. Thus the position of the stylus relative to the drivenelectrodes, using known interpolation techniques, may be determined.Coordinating the activities of the stylus drive and stylus receive modesis effected via the communication lines 920 by controller 114.

FIG. 11a a swim lane flowchart illustrating the interaction and driveand receive modes of the stylus and touch panel implementing theembodiments and methods described with respect to FIG. 10 during a fullmeasurement sequence (which includes driving all driven electrodes oftouch panel 112 plus the stylus drive electrode). This example assumeseach receive electrode is coupled to receive electronics as describedwith respect to FIG. 3a , though other receive electronics describedwith respect to other embodiments described with respect to FIG. 3bthrough 3e are contemplated. The left swim lane in FIG. 11a representsprocess steps in the stylus, and the right swim lane represents processsteps in the touch panel. Certain coordinating and calculationactivities of controller 114 are not shown in this figure and aredescribed. FIG. 11b is a simplified touch panel that will be referred toin the sequence of FIG. 11a . FIG. 11b has two driven electrode (D1 andD2) and two receive electrodes (R1 and R2). Assume a stylus tip is atposition S, and a finger is touching at position F.

The measurement sequence starts (1100) with the stylus in driven mode,and the stylus electrode driven (1110). As mentioned above, this couldbe with a series of square or ramped pulses, for example, the same orsimilar drive waveforms that are used to drive the driven electrodes oftouch panel 112. Each wave will form a coupling capacitance C_(c) on thereceive electrode associated with R1, but not R2. Next, the stylusswitches to receive mode (1112), and R1 and R2 are queried (1112B). Thevoltage in peak detect unit 326 a (FIG. 3a ) for R1 will be high,whereas the voltage in the peak detect unit for R2 will be low.Controller 114 may use this information to compute that the stylus tipis located proximate to the R1 electrode. Next, the driven electrodes inthe touch panel are sequentially driven. This starts with applying oneor more ramped or square wave pulses to D1, consistent with thedescription for embodiments described above with respect to FIGS. 3athrough 3e . After D1 is driven, voltages associated peak amplitudes oneach receive electrode (in this case R1 and R2) are queried by ADC unit324 (referring once again to FIG. 3a ) (step 1414B). A lower peakvoltage would be seen on R2 than on R1, due to finger touch T reducingcoupling capacitance C_(c) at the D1-R2 node. Controller may compute thepresence of a non-stylus touch at D1-R2. Next, the stylus receiveelectrode is queried (step 1116A) by inspecting the stylus peak detectunit 3326 a. Since stylus electrode is positioned at position S in FIG.11B, no (or relatively, very little) coupling capacitance C_(c) isformed between the stylus electrode and the driven electrode D1 (thatwas driven in step 1114B), thus the associated amplitude of stylus senseunit would be low. Controller 114 may computer, based on thisinformation, that there is no stylus at node D1-R1. Next, D2 is driven(1118B) in a manner similar to how D1 was driven in step 1114B. R1 andR2 are then queried (1120B) in a manner similar to step 1114B. Data fromthese two steps would allow controller 114 to compute that there existno finger touches along the D2 electrode. Next, to complete the fullmeasurement cycle, the stylus electrode is again queried in step 1122A(which is the same as step 1116A), but this time stylus peak detect unit3326 a would show a relatively higher voltage, which controller 114would use to calculate that the stylus electrode is closest to the nodeD2-R1 node. The process then repeats.

This process may be adapted to accommodate multiple styli by controller114 coordinating additional electrode drive steps (such as step 1110),in a manner further described later with respect to FIG. 12. The portionof the process wherein the stylus is acting as a receive electrode wouldnot change, as each stylus would independently be able to couple to adriven electrode and have positional information related to one axisderived therefrom. That is, even supporting multiple styli, there wouldstill only need to be one sequential driving of the driven electrodes inthe touch panel, and resulting data from each stylus in contact with thetouch panel could be used to determine the position of the respectivestylus along the drive electrodes. Additional stylus drive sequences,however, would need to be added by controller 114 for each supportedstylus. This could be accomplished by appropriately modifying thefirmware of controller 114. As the driven electrodes of the touch panelare sequentially driven, each pen would receive a pulse that istemporally associated with a respective driven electrode thus definingone of the coordinates (X or Y, depending on how the system isoriented). After all of the driven electrodes have been driven, eachpen, in sequence, would drive its respective stylus electrode while thereceive electronics of the touch panel listens on each receiveelectrode. The receive electronics would be re-set, then the next penpulses down, and so forth until all pens have pulsed downward. Eachadditional pen would require an additional drive cycle (for the pen) andcorresponding receive cycle for the touch panel and its electronics.

This process represented in FIG. 11A may of course be modified in thespirit of this disclosure, the steps done in different orders, but thebasic process is presented herein, and such modifications are intendedto be within the scope of this disclosure. Controller 114's calculationof the precise location of stylus touch point S and finger touch point F(FIG. 11B) could be enhanced using known interpolation techniques, giventhe coupling capacitances at proximate nodes, or using data from forexample accelerometer 904 (which could be used to determine the angle ofthe stylus tip).

Stylus as Drive Electrode Only

In another embodiment, the stylus may be integrated with theabove-described multi-touch sensitive systems by configuring the stylustip electronics 907 with a stylus drive unit. The stylus drive unitwould be the same or similar to that described with respect to theembodiment shown with respect to FIG. 10, and would be configured in thesame or a way similar to described in regards to that embodiment. Thestylus in such an embodiment would not include the stylus receiveelectronics.

In such an embodiment, the electronics associated with the touch panelwould need to be modified to, in one embodiment, essentially let thedriven electrodes be switched to act either as driven electrodes or asanother set of receive electrodes. For example, referring to the simpletouch panel representation of FIG. 11b , each receive electrode iscoupled to receive electronics, several embodiments of which aredescribed above with respect to FIGS. 3a through 3e . After each driveelectrode (D1, then D2) is driven, receive electronics associated witheach receive electrode are queried, and resultant touch informationderived. To accommodate a stylus that acts as a drive electrode, itsposition with respect to the receive electrodes (R1 and R2) may bedetermined in the same or similar manner as described above with respectto “Stylus as Drive Electrode and Receive Electrode.” However, in orderto determine the position of the stylus electrode relative to the drivenelectrodes (D1 and D2), in this embodiment the drive electrodes areswitched to the receive electronics associated with R1 and R2, which“listen” when as the stylus electrode is driven. The receiveelectronics, now associated with D1 and D2, may then be queried todetermine the position of the stylus electrode relative to D1 and D2.

The coupling of the driven electrodes to receive electronics may beaccomplished in several ways. As described above, there may be a switchemployed such that the same receive electronics that serve the receiveelectrodes may be utilized to “listen” on the drive electrodes.Alternatively, or additionally, a portion or all of the drive electrodesmay have their own dedicated receive electronics.

FIG. 12 is a flowchart illustrating a representative drive cycle of anembodiment where the stylus acts as a drive electrode only, incombination with a touch panel as described above. Reference is made tothe simplified rendering of a touch panel in FIG. 11b . An initial driveelectrode (D1) is driven (step 1205). The receive electrodes are thenprocessed (step 1210), in a manner consistent with any of the embodimentdescribed above with respect to FIG. 3a through 3e , which yields dataindicative of touches along the D1 drive electrode (step 1215). In thecase of the touch panel shown with respect to FIG. 11B, the electronicsassociated with receive electrode R2 would show a surrogate (such asvoltage, in the case of the embodiments shown in FIG. 3a ) of couplingcapacitance at node D1-R2 that is lower than other nodes along D1,indicating a touch at position F. If there are more drive electrodes inthe touch panel (yes at step 1220), the process moves on to the nextdrive electrode D2 (step 1225) and the process repeats until all drivenelectrodes in the touch panel have been driven (no at step 1220), andreceive electronics subsequently processed, yielding positioninformation. This process yields information indicative of thecoordinates of all conventional touches to the touch screen, be it oneor many simultaneous or temporally overlapping finger touches.

With all touch panel drive electrodes sequentially driven and alltouches to the touch panel resolved, controller 114 proceeds to stylussupport mode (no at step 1220) to resolve the coordinates of one or manystyli in proximity to the touch panel. The driven electrodes (D1 and D2)are switched by controller 114 to be coupled to receive electronics(step 1230) of the type used with R1 and R2, or possibly any type asdescribed with respect to FIGS. 3a through 3e . Effectively, D1 and D2become additional receive electrodes similar to R1 and R2. Controller114 then signals the first stylus to drive its stylus electrode (step1235). The receive electrodes R1 and R2 would then be processed asdescribed above, and the driven electrodes D1 and D2 that were put intoreceive mode would also be similarly processed (step 1240). Thisprocessing would sense a higher coupling capacitance to form along nodeR1, and also to forma long D2, indicating a stylus electrode inproximity to node D2-R1 (step 1245). If there are more styli (yes atstep 1250), the next stylus (step 1255) is selected by controller 114,and the process repeats until all styli known by controller 114 havebeen driven (no at 1250). Then the driven electrodes are de-coupled fromthe receive electronics, or otherwise put back into their native drivemode (step 1260) and the entire process repeats.

This process assumes separate, non-shared receive electronics may becoupled to the drive electrodes D1 and D2, which allows for each stylusto be driven only once. In such a configuration (or any configurationdiscussed herein), the stylus may in fact be configured to drivemultiple times to improve signal to noise ratios. In another embodiment,however, the receive electronics are shared between the receiveelectrodes and the drive electrodes. In such an embodiment, the locationof the stylus along the receive access (R1 and R2) is developed by afirst signal provided by the stylus, then the driven electrodes D1 andD2 are coupled to the receive electronics associated with R1 and R2, toreceive a subsequent signal from the stylus and thus develop thelocation of the stylus along the driven electrode axis (D1 and D2). Thisapproach has the benefit of reducing the receive electronics, but addsan additional drive step for each stylus.

Multiple styli are supported by programming the controller's firmware tocoordinate sequential pulsing of each pen, corresponding to a receivesequence for each axis of the touch panel. For example, a first styluselectrode would be driven, and the receive electronics associated withone of the touch panel's axis would be evaluated, then the first styluselectrode would again be driven, and receive electronics associated withthe other one of the touch panel's axis would be evaluated. Then theprocess would repeat for all successive supported styli, withappropriate re-setting of the receive electronics as necessary. In someembodiments, for example where the receive electronics associated withrespective X- or Y-electrode sets are not shared, a single drivesequence provided to the stylus electrode may provide both the X- andthe Y-coordinate.

Stylus as Receive Electrode Only

In another embodiment, the stylus may be integrated with above-describedmulti-touch sensitive systems by configuring the stylus tip electronics907 with stylus receive electronics. The stylus receive electronicswould be the same or similar to the receive portion of the electronicsdescribed with respect to the embodiment shown with respect to FIG. 10,and would be configured in the same or a similar manner as describedwith respect to that embodiment. The stylus in such an embodiment wouldnot need to include the stylus drive electronics.

In such an embodiment, the electronics associated with the touch panelwould need to be modified to, in one embodiment, essentially allow thereceive electrodes to be sequentially driven, the same or similar to themanner in which the drive electrodes are sequentially driven. Forexample, referring to the simple touch panel representation of FIG. 11b, each drive electrode D1 and D2 would be coupled to a drive unit(likely with a multiplexer in between). The receive electrodes R1 and R2are coupled to receive electrodes, several embodiments of which aredescribed with respect to FIGS. 3a through 3e . After each driveelectrode is driven, the coupling capacitances formed on each thereceive electrodes is processed by controller 114, the receiveelectronics reset, and the next drive electrode driven, etc, until alldrive electrodes have been driven. This process is the same as what hasbeen described above with respect to multi-touch system operation withrespect to FIGS. 3a through 3e . The stylus electrode, if proximate todriven electrodes in the touch panel, will couple to particular driveelectrodes to which the stylus electrode is proximately located. Thestylus microprocessor 901 may send data indicative of a couplingcapacitance between the stylus electrode and a particular one of thetouch panel drive electrodes after each touch panel drive electrodedrive sequence, such that controller 114 may compute where the styluselectrode is located (and again may further employ known interpolationtechniques for higher precision). In another embodiment, the controller114 signals to microprocessor 901 when an entire drive cycle (includingall driven electrodes) is beginning (t=0), then the microprocessor 901would report back the time offset value (t+x) when a couplingcapacitance value above some threshold was measured using the stylusreceive electronics in tip electronics 907. After the all drivenelectrodes are driven in sequence, the time offset values of allcapacitances above a threshold (as well as data indicative of suchcapacitances) may be provided to controller 114 by microprocessor 901,which controller 114 may then use to determine which driven electrodesthe offsets are associated with. Once all driven electrodes of the touchpanel have been so driven, the receive electrodes of the touch panel aresequentially driven, in one embodiment through the use of a multiplexercoupled between the drive unit and each receive electrode. The touchpanel receive electrodes then are sequentially driven, and a couplingcapacitance formed with the stylus electrode, and reported back tocontroller 114 similar to the manner in which the stylus electrodeposition relative to the driven electrodes was determined.

After a full drive cycle (comprising sequentially driving the touchpanel drive electrodes and then sequentially driving the touch panelreceive electrodes), controller 114 may determine the coordinates of thestylus electrode relative to the touch panel's receive and driveelectrodes.

Note that in the embodiment just described, the same sequence determinesthe positions of any traditional touches (as with a finger) as well asthe location of the stylus with respect to the touch panel's drivenelectrodes. In some embodiments, the coupling capacitance that is formedwith the stylus electrode may negatively impact a finger locatedproximate to the same driven electrode, because the coupling of thestylus may introduce artifacts into the signal used for detecting fingertouches. In another embodiment, this is addressed by having a dedicatedfinger drive sequence (where the stylus is not “listening) as describedwith respect to any of the embodiments associated with FIGS. 3a through3e , then driving the touch panel driven electrodes again (where thestylus is listening, but the touch panel's receive electronics arepossibly not queried and reset after each drive sequence, which wouldmean the drive sequence could be faster), and then a third drivesequence wherein the touch panel receive electronics are sequentiallydriven while the stylus is again in listening mode.

FIG. 13 is a flowchart illustrating a representative drive cycle of anembodiment where the stylus acts as a receive electrode only (as opposedto earlier described embodiments in which the stylus acted as both areceive and drive electrode, or just a drive electrode), in combinationwith a touch panel as described above. Reference is made to thesimplified rendering of a touch panel in FIG. 11b . An initial driveelectrode (D1) is driven (step 1305). The receive electrodes are thenprocessed (step 1310), in a manner consistent with any of theembodiments described above with respect to FIG. 3a through 3e , whichyields data indicative of touches along the D1 drive electrode (step1315). In the case of the touch panel shown with respect to FIG. 11B,the electronics associated with receive electrode R2 would show asurrogate (such as voltage, in the case of the embodiment shown in FIG.3a ) of coupling capacitance at node D1-R2 that is lower than othernodes along D1, indicating a touch at position F. The stylus receiveelectronics are also processed (also in steps 1315), because if thestylus electrode is sufficiently close to D1, a coupling capacitancewould form and be sensed by stylus microprocessor 901 in combinationwith the stylus receive electronics. In the case of the driving of D1,no coupling capacitance above a threshold value is formed with thestylus electrode because the stylus electrode is too far away from D1.If there are more drive electrodes in the touch panel (yes at step1320), the process moves on to the next drive electrode D2 (step 1325)and the process repeats until all driven electrodes in the touch panelhave been driven (no at step 1320), yielding touch-related information,as described in detail earlier in this description. When electrode D2 isdriven, a coupling capacitance between electrode D2 and the styluselectrode is formed due to the stylus electrode being at position S, andthis is sensed by the stylus receive electronics, and reported bymicroprocessor 901 to controller 114 either via radio 903 or via someother connection, such as universal serial bus or other wiredconnection. With this information, controller 114 has information onlysufficient to infer that a stylus is located somewhere along D2, butdoes not know if that somewhere is closer to receive electrode R1 or R2.Thus, before proceeding to the remainder of the process (no at 1320),controller 114 has enough data to determine the position of all fingertouches (or anything that would reduce coupling capacitance at a node),and partial data as to the position of the stylus.

The remainder of the process shown in FIG. 13 concerns developing theadditionally needed information concerning the location of styluselectrode along receive electrode R1 and R2. This information isdeveloped by sequentially driving the touch panel's receive electrode R1and R2 in a manner similar to or the same as D1 and D2 were driven.Thus, controller 114 provides signals that turn first R1 into a driveelectrode by coupling electrode R1 with a drive unit. In one embodimentthe drive unit is the same as that which is used to drive touch paneldriven electrodes D1 and D2, and the connection occurs via a switch or amultiplexer. When R1 is driven (step 1330), a coupling capacitance isformed on the stylus electrode that is located at position S. Thisinformation will be reported back to controller 114 by microprocessor901 in ways earlier described, which will reveal that the styluselectrode is at position S (step 1335). The process continues for eachtouch panel receive electrode (decision at 1340) until all touch panelreceive electrodes have been driven, at which point the process repeats(no at 1340).

Multiple styli may be supported without modifying the basic driveroutine. Each stylus would signal when it had coupled with signalemanating from the sensor, and controller 114 would associate couplingwith the electrode previously driven, and thereby establish coordinatetype information for one stylus or a plurality of styli.

With regard to all of the stylus-related embodiments described herein,they have generally been described with respect to a peak-detect typecircuit. In other embodiments, the same concepts may be used with other,more traditional circuits, including those that integrate (rather thanpeak detect) the received signal, and in such way determine a couplingcapacitance between two electrodes.

Further, embodiments have been described having various electroniccomponents within the stylus housing. It is to be understood that thestylus electrode is the only thing needing to be in the stylus housing;remaining components may be all physically arranged outside of thestylus housing.

Unless otherwise indicated, all numbers expressing quantities,measurement of properties, and so forth used in the specification andclaims are to be understood as being modified by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and claims are approximations that canvary depending on the desired properties sought to be obtained by thoseskilled in the art utilizing the teachings of the present application.Not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the invention are approximations, to the extent any numerical valuesare set forth in specific examples described herein, they are reportedas precisely as reasonably possible. Any numerical value, however, maywell contain errors associated with testing or measurement limitations.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the spirit and scopeof this invention, and it should be understood that this invention isnot limited to the illustrative embodiments set forth herein. Forexample, the reader should assume that features of one disclosedembodiment can also be applied to all other disclosed embodiments unlessotherwise indicated. It should also be understood that all U.S. patents,patent application publications, and other patent and non-patentdocuments referred to herein are incorporated by reference, to theextent they do not contradict the foregoing disclosure.

What is claimed:
 1. A touch sensitive system comprising: a touch panelcomprising a transparent capacitive sensing medium including a first setof electrodes and a second set of electrodes arranged to form a matrixand an insulating layer arranged between the first set of electrodes andthe second set of electrodes, the matrix having a plurality of nodesdefined by areas on a touch surface of the transparent capacitivesensing medium where the first set of electrodes and the second set ofelectrodes traverse one another; a stylus electrode arranged in a stylushousing; a stylus drive unit configured to provide a stylus drive signalto the stylus electrode; a touch panel sense unit configured togenerate, for each stylus drive signal provided to the stylus electrode,if capacitively coupled to an electrode in the touch panel, touch panelresponse signals, each of the touch panel response signals comprising adifferentiated representation of the stylus drive signal, thedifferentiated representation of the stylus drive signal being an outputsignal of a differentiation circuit, the output signal beingsubstantially a derivative with respect to time of an input signalreceived by the differentiation circuit, the input signal beingindicative of the stylus drive signal, an amplitude of each of theresponse signals being responsive to the coupling capacitance betweenthe stylus electrode and at least one electrode in the touch panel, theamplitude of the response signals being substantially linearlyproportional to the coupling capacitance; a measurement unit configuredto measure or receive input indicative of the amplitude of the touchpanel response signals and to determine therefrom the position of thestylus, if present, on the touch surface.
 2. The touch sensitive systemof claim 1, wherein the touch panel sense unit is communicativelycoupled to both the first and the second set of electrodes by way of oneor more communication wires.
 3. The touch sensitive system of claim 2,wherein the first and the second sets of electrodes each comprise aplurality of electrodes.
 4. The touch sensitive system of claim 3,further comprising a touch panel multiplexer to communicatively couplethe touch panel sense unit with electrodes in either the first or thesecond sets of electrodes.
 5. The touch sensitive system of claim 3,further comprising a plurality of additional touch panel sense units,the number of additional touch panel sense units equal to the greaterof: (1) the number of electrodes in the first set of electrodes; or (2)the number of electrodes in the second set of electrodes.
 6. The touchsensitive system of claim 5, wherein each touch panel sense unit iscoupled to all electrodes that comprise the first set of electrodes, andeach generates response signals, if any at all, for each drive signal,simultaneously or approximately simultaneously.
 7. The touch sensitivesystem of claim 1, wherein the measurement unit is communicativelycoupled to the stylus drive unit.
 8. The touch sensitive system of claim7, further comprising: control logic associated with the measurementunit that coordinates activity of the stylus drive unit and the touchpanel sense unit such that a stylus drive signal is delivered to thestylus electrode while the touch panel sense unit is configured togenerate response signals for the first set of electrodes, then asubsequent stylus drive signal is delivered to the stylus electrodewhile the touch panel sense unit is configured to generate responsesignals associated with the second set of electrodes.
 9. The touchsensitive system of claim 1, further comprising: a stylus processor unitcommunicatively coupled to the stylus drive unit, and mechanicallycoupled to the stylus housing, and wherein the stylus drive unit ismechanically coupled to the stylus housing, and further wherein thestylus processor unit is communicatively coupled to the measurement unitand is configured to receive from the measurement unit information tocoordinate the functionality of the stylus drive unit.
 10. The touchsensitive system of claim 1, wherein the stylus drive signal comprises aseries of digital pulses, at least some having frequencies differentfrom others.
 11. The touch sensitive system of claim 1, wherein thestylus drive signal comprises a single pulse.
 12. The touch sensitivesystem of claim 11, wherein the single pulse comprises a square wave.13. The touch sensitive system of claim 10, wherein the stylus drivesignal comprises a series of digital pulses having differing dutycycles.
 14. The touch sensitive system of claim 1, wherein the touchpanel sense unit includes a peak detector configured to provide a peakdetector output representative of a maximum amplitude of the respectivetouch panel response signal.
 15. The touch sensitive system of claim 14,wherein the peak detector comprises a diode coupled to a capacitor. 16.The touch sensitive system of claim 14, wherein the peak detectorcomprises a sample/hold buffer.
 17. The touch sensitive system of claim1, wherein the differentiation circuit includes an operational amplifierhaving an inverting input coupled to an electrode in the first or secondset of electrodes.
 18. The touch sensitive system of claim 17, whereinthe differentiation circuit includes a feedback resistor connectedbetween the inverting input and an output of the operational amplifier.19. The touch sensitive system of claim 18, wherein the inverting inputis adapted to receive the input signal and the output of the operationalamplifier is adapted to provide the output signal.